The potential across a generator is 125V when it is delivering 10A. When it delivers 30A the potential is 120V. What are the resistance of armature and induced e.m.f. ?

Question

The potential across a generator is 125V when it is delivering 10A. When it delivers 30A the potential is 120V. What are the resistance of armature and induced e.m.f. ? (A) 5Ω,127.5V (B) 0.25Ω,127.5V (C) 2.5Ω,120V (D) 5Ω,130V

Tardigrade Admin · Accepted Answer

Using V = E - ir , we get, 125 = E - 10r ....(i) and 120 = E - 30r ...(ii) Subtracting (ii) from (i), 5 = 20r or r = 0.25Ω from (i) 125 = E - (10 × 0.25) or E = 125 + 2.5 = 127.5 V

Q. The potential across a generator is 125V when it is delivering 10A. When it delivers 30A the potential is 120V. What are the resistance of armature and induced e.m.f. ?

$5Ω, 127.5 V$

$0.25Ω, 127.5 V$

$2.5Ω, 120 V$

$5Ω, 130 V$

Using V = E - $i r$ , we get, 125 = E - 10r .... $(i)$
and 120 = E - 30r ... $(ii)$
Subtracting $(ii)$ from $(i)$ , 5 = 20 $r$ or $r$ = 0.25 $Ω$
from $(i)$ 125 = E - (10 $\times$ 0.25)
or E = 125 + 2.5 = 127.5 V